Electroless plating method and ceramic substrate

ABSTRACT

Provided is an electroless plating method for a low temperature co-fired glass ceramic substrate, the method including: a degreasing and activation treatment step of degreasing and activating a surface of a wiring pattern formed of a silver sintered body; a catalyzing step of providing a catalyst onto the surface of the wiring pattern formed of a silver sintered body; and an electroless multi-layered coating plating treatment step. The electroless plating method further includes, between the degreasing and activation treatment step and the catalyzing step, a silver precipitation treatment step of precipitating silver on a glass component present on the surface of the wiring pattern formed of a silver sintered body after the degreasing and activation treatment step, and the catalyzing step includes providing the catalyst also to the silver precipitated in the silver precipitation treatment step.

TECHNICAL FIELD

The present invention relates to an electroless plating method forforming a plating coating on a surface of a wiring pattern in a glassceramic substrate, in particular, a LTCC substrate to be used for anelectronic component package or a wiring board, and to a ceramicsubstrate.

BACKGROUND ART

A ceramic substrate has hitherto widely been used for a wiring board fora multi-chip module package in which a plurality of semiconductorelements and a plurality of passive elements such as a capacitor and aresistor are mounted. A low temperature co-fired glass ceramic substrate(LTCC substrate), which is obtained by firing at low temperature, or thelike is used as the ceramic substrate. The “low temperature” in the caseof the low temperature co-fired glass ceramic substrate refers to atemperature range of from 850° C. to 1,000° C. The LTCC substrateincludes an insulating base material formed of glass ceramic, and awiring pattern formed of a sintered body containing as a main componenta metal material (for example, silver) (wiring pattern formed of asilver sintered body).

The wiring pattern formed of a silver sintered body in the LTCCsubstrate is electrically connected to a semiconductor element or apassive element by wire bonding, and then connected to a printed boardmade of a resin serving as an external electrical circuit via solder. Ingeneral, a multi-layered electroless plating coating that satisfies botha wire bonding property and solderability necessary for the connectionis formed on a surface of the wiring pattern. As constituents of themulti-layered electroless plating coating, a nickel plating coating, agold plating coating, and in recent years, a palladium plating coatinghave been known.

As a method of forming the nickel plating coating, the gold platingcoating, and the palladium plating coating selectively on the wiringpattern formed of a silver sintered body in the LTCC substrate,electroless plating has been widely used. The electroless platinggenerally involves a plurality of steps including a surface activationstep, a catalyzing step, and a plurality of electroless plating steps offorming a multi-layered plating coating including an electroless nickelplating coating and the like.

In association with formation of the plating coating on the surface ofthe wiring pattern formed of a silver sintered body in the LTCCsubstrate, it has hitherto been known that, at the time of firing of thesubstrate, a phenomenon called glass floating, in which a glasscomponent is formed on the surface of the wiring pattern formed of asilver sintered body, may occur. When the glass floating occurs, anon-plating state, in which the nickel plating coating is prevented frombeing formed on the glass component, may occur, or the plating coatingmay have an uneven thickness.

As a method of preventing such non-plating state, there has hithertobeen known, for example, a method involving, between the surfaceactivation step and the catalyzing step, a step of removing the glasscomponent present on a surface to be subjected to electroless plating byusing a pretreatment agent containing a reducing agent (see, forexample, Patent Literature 1).

CITATION LIST Patent Literature

[PTL 1] JP 2005-68489 A

SUMMARY OF INVENTION Technical Problem

However, the related-art electroless plating method disclosed in PatentLiterature 1 has the following problems.

The amount of the glass component to be contained in the wiring patternformed of a silver sintered body generally varies depending on thecombination of the wiring pattern formed of a silver sintered body andLTCC substrate to be used. The glass component formed on the surface ofthe wiring pattern formed of a silver sintered body owing to the glassfloating varies in size depending on the combination of the wiringpattern formed of a silver sintered body and LTCC substrate to be used.When the glass component has a size exceeding 1 μm, the glass componentmay fail to be removed. In addition, when the glass component fails tobe removed, non-plating, in which the nickel plating coating isprevented from being formed on the glass component, may occur.

In addition, when a glass component having a size exceeding 1 μm to 5 μmis removed, a recess may be generated in the surface of the wiringpattern formed of a silver sintered body. Further, when a recess isgenerated in the surface of the wiring pattern formed of a silversintered body, the plating coating may be unevenly distributed, or voidsmay be generated in the plating coating. Further, when voids aregenerated in the plating coating, there is a risk in that a platingliquid or washing liquid used during electroless plating is taken in thevoids, and its water content vaporizes during solder connection, whichresults in solder connection failure. This leads to a reduction inmodule reliability.

The present invention has been made for solving the above-mentionedproblems, and an object of the present invention is to provide anelectroless plating method and ceramic substrate, which preventnon-plating of the nickel plating coating, and suppress the formation ofvoids in the plating coating and accompanying solder connection failure,and thus realize improved module reliability.

Solution to Problem

According to one embodiment of the present invention, there is providedan electroless plating method for a low temperature co-fired glassceramic substrate including an insulating base material formed of glassceramic, and a wiring pattern formed of a silver sintered body, theelectroless plating method including: a degreasing and activationtreatment step of degreasing and activating a surface of the wiringpattern formed of a silver sintered body; a catalyzing step of providinga catalyst onto the surface of the wiring pattern formed of a silversintered body after the degreasing and activation treatment step; and anelectroless multi-layered coating plating treatment step of forming amulti-layered electroless plating coating on the surface of the wiringpattern formed of a silver sintered body on which the catalyst isprovided, the electroless plating method further including, between thedegreasing and activation treatment step and the catalyzing step, asilver precipitation treatment step of precipitating silver on a glasscomponent present on the surface of the wiring pattern formed of asilver sintered body after the degreasing and activation treatment step,the catalyzing step including providing the catalyst also to the silverprecipitated in the silver precipitation treatment step.

In addition, a ceramic substrate according to one embodiment of thepresent invention includes a multi-layered electroless plating coatingformed by an electroless plating method for a glass ceramic substrateincluding an insulating base material formed of glass ceramic, and awiring pattern formed of a silver sintered body, the method including: adegreasing and activation treatment step of degreasing and activating asurface of the wiring pattern formed of a silver sintered body; a silverprecipitation treatment step of precipitating silver on a glasscomponent present on the surface of the wiring pattern formed of asilver sintered body after the degreasing and activation treatment step;a catalyzing step of providing a catalyst onto the surface of the wiringpattern formed of a silver sintered body after the silver precipitationtreatment step; and an electroless multi-layered coating platingtreatment step of forming a multi-layered electroless plating coating onthe surface of the wiring pattern formed of a silver sintered body onwhich the catalyst is provided.

Advantageous Effects of Invention

The electroless plating method according to one embodiment of thepresent invention can achieve the electroless plating method and ceramicsubstrate, which prevent non-plating of the nickel plating coating, andsuppress the formation of voids in the plating coating and accompanyingsolder connection failure, and thus realize improved module reliability,because the silver precipitation treatment step of precipitating silveron a glass component present on the surface of the wiring pattern formedof a silver sintered body is included between the degreasing andactivation treatment step and the catalyzing step.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a process flow according to a first embodiment of thepresent invention.

FIG. 2 is a sectional view illustrating a glass ceramic wiring board tobe used in the first embodiment of the present invention.

FIG. 3 is an enlarged view illustrating a state of a glass componentportion formed on the surface of a wiring pattern formed of a silversintered body of FIG. 2 after a silver precipitation treatment step.

FIG. 4 is an electron micrograph showing the surface of the wiringpattern formed of a silver sintered body after the silver precipitationtreatment step of the present invention.

FIG. 5 is a sectional view illustrating a state in which the surface ofthe wiring pattern formed of a silver sintered body after a catalyzingstep has been subjected to an electroless nickel plating step.

FIG. 6 is an enlarged view illustrating the glass component portion ofFIG. 5 formed on the surface of the wiring pattern formed of a silversintered body.

FIG. 7 is a sectional view illustrating a state in which the surface ofthe wiring pattern formed of a silver sintered body in the state of FIG.5 has been subjected to an electroless palladium plating step.

FIG. 8 is a sectional view illustrating a state in which the surface ofthe wiring pattern formed of a silver sintered body in the state of FIG.7 has been subjected to a substitution-type electroless plating step.

FIG. 9 illustrates a process flow according to a second embodiment ofthe present invention.

FIG. 10 illustrates a process flow according to a third embodiment ofthe present invention.

FIG. 11 is a sectional view illustrating a state in which the surface ofthe wiring pattern formed of a silver sintered body of FIG. 9 has beensubjected to a substitution-type electroless gold plating step and areduction-type electroless gold plating step.

FIG. 12 illustrates a process flow according to a fourth embodiment ofthe present invention.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 1 illustrates a process flow according to a first embodiment of thepresent invention. An electroless plating method for a glass ceramicwiring board of FIG. 1 includes performing, on the surface of a wiringpattern formed of a silver sintered body, a degreasing and activationstep (Step S101), a catalyzing step (Step S103), an electroless nickelplating step (Step S1041), an electroless palladium plating step (StepS1042), and a substitution-type electroless gold plating step (StepS1043). The electroless plating method of FIG. 1 further includesperforming a silver precipitation treatment step (Step S102) between thedegreasing and activation step and the catalyzing step.

The electroless nickel plating step (Step S1041), the electrolesspalladium plating step (Step S1042), and the substitution-typeelectroless gold plating step (Step S1043) are collectively referred toas electroless multi-layered coating plating treatment step (Step S104).

FIG. 2 is a sectional view illustrating a glass ceramic wiring board tobe used in the first embodiment of the present invention. As illustratedin FIG. 2, a glass ceramic wiring board (LTCC substrate) generallyincludes an insulating base material 1 formed of glass ceramic, and awiring pattern 2 formed of a metal sintered body. The glass ceramic ispreferably oxide-based ceramic formed of silicon dioxide, alumina, orthe like. The wiring pattern 2 formed of a metal sintered body isappropriately designed depending on a desired electronic componentpackage or wiring board. In addition, a metal sintered body for formingthe wiring pattern 2 formed of a metal sintered body is selected so thatcharacteristics required for an electronic component or the like to besubjected to electroless plating are satisfied. In the presentinvention, a silver-palladium alloy containing silver is used for themetal sintered body.

The wiring pattern 2 formed of a metal sintered body is hereinafterreferred to as wiring pattern 2 formed of a silver sintered body. Aglass component 3 is formed on the surface of the wiring pattern 2formed of a silver sintered body.

Next, the steps are each described in detail.

<Degreasing and Activation Step>

First, in the degreasing and activation step of Step S101, an organicmaterial, an oxide coating, or the like is removed from the surface ofthe wiring pattern 2 formed of a silver sintered body.

<Silver Precipitation Treatment Step>

Next, the silver precipitation treatment step is described withreference to FIG. 3. FIG. 3 is an enlarged view illustrating a state ofthe glass component 3 portion formed on the surface of the wiringpattern 2 formed of a silver sintered body of FIG. 2 after the silverprecipitation treatment step.

In the silver precipitation treatment step of Step S102, a silvercomponent in the glass component 3 present on the surface of the wiringpattern 2 formed of a silver sintered body is dissolved without damagingthe wiring pattern 2 formed of a silver sintered body, and silverparticles 4 are redeposited on the glass component 3, as illustrated inFIG. 3. That is, the silver precipitation treatment step is a step ofprecipitating the silver particles 4 on the glass component 3 present onthe surface of the wiring pattern 2 formed of a silver sintered bodythat has been cleaned and activated in Step S101 by immersion indegreasing and activation treatment liquids.

The inventors of the present invention have found that the silverparticles 4 have a property of being precipitated selectively on theglass component 3 present on the surface of the wiring pattern 2 formedof a silver sintered body, as illustrated in FIG. 3, by treating thesurface of the wiring pattern 2 formed of a silver sintered body with asilver precipitation treatment liquid before providing a catalyst.

As the silver precipitation treatment liquid to be used in the silverprecipitation treatment step, there may be used, for example, a silverprecipitation treatment liquid containing 1 to 10 wt % of a reducingagent and 5 to 15 wt % of a complexing agent such as citric acid, malicacid, or succinic acid, and having a pH adjusted to from 4 to 6 withsulfuric acid or sodium hydroxide.

For example, the reducing agent preferably contains any one of thefollowing first reducing agents, or the first reducing agent and thefollowing second reducing agent in combination. Preferred examples ofthe first reducing agent include a phosphoric acid compound and anorganic acid. In addition, a preferred example of the second reducingagent is an inorganic compound.

Hypophosphorous acid, sodium hypophosphite, or potassium hypophosphiteis preferably used as the phosphoric acid compound.

Formic acid or citric acid is preferably used as the organic acid.

Iron(II) chloride, iron(II) sulfate, or sodium thiosulfate is preferablyused as the inorganic compound.

The silver precipitation treatment liquid more preferably contains, asthe first reducing agent, 1 to 10 wt % of hypophosphorous acid, sodiumhypophosphite, or potassium hypophosphite, or 1 to 10 wt % of formicacid or citric acid. In addition, the silver precipitation treatmentliquid preferably contains, as the second reducing agent, 1 to 100 ppmof iron(II) chloride, iron(II) sulfate, or sodium thiosulfate.

The silver precipitation treatment conditions are described below. Theimmersion time period for which the LTCC substrate is immersed in thesilver precipitation treatment liquid is not particularly limitedbecause the immersion time period is affected by the liquid temperature,treatment time period, and concentration of a catalyst providing liquidor nickel plating treatment liquid, but is generally preferably from 1to 10 minutes. In addition, the liquid temperature of the silverprecipitation treatment liquid is not particularly limited as long assilver can be precipitated, but is preferably adjusted to from 80° C. to90° C. from the viewpoint of silver precipitation efficiency.

The silver precipitation treatment liquid is preferably used in theabove-mentioned temperature range, but may be used by appropriatelyadjusting the liquid temperature in accordance with the state of theLTCC substrate. The silver precipitation treatment liquid is acidic.

The silver component, which has been diffused through firing, is presentin the glass component 3 formed on the surface of the wiring pattern 2formed of a silver sintered body owing to glass floating. The silvercomponent is exposed by etching the surface of the glass component 3 ina trace amount with the silver precipitation treatment liquid, anddissolved and ionized in the silver precipitation treatment liquid byvirtue of its acidity. Silver dissolved in the silver precipitationtreatment liquid is deposited selectively on the glass component 3present around the wiring pattern 2 formed of a silver sintered body, asillustrated in FIG. 3. The deposits are the silver particles 4. Silverdissolved in the silver precipitation treatment liquid is redeposited ina short time, and hence is prevented from being diffused in thetreatment liquid.

That is, the silver component is instantly dissolved and redeposited, tobe deposited almost selectively only on the glass component 3 present onthe surface of the wiring pattern 2 formed of a silver sintered body,and on a white plate (glass) portion within 1 to 10 μm from the wiringpattern 2 formed of a silver sintered body. FIG. 4 is an electronmicrograph showing the surface of the wiring pattern formed of a silversintered body after the silver precipitation treatment step of thepresent invention. The glass component 3 is present in an upper rightportion of FIG. 4. In addition, portions observed as white spotsthroughout FIG. 4 are the precipitated silver particles 4.

As shown in FIG. 4, the silver particles 4 are each deposited in aparticulate form on the glass component 3. In addition, the silverparticles 4 each have a particle size of from 10 to 100 nm.

<Catalyzing Step>

Next, in the catalyzing step of Step S103, the LTCC substrate isimmersed in a catalyst liquid containing palladium or the like, toprovide a palladium catalyst onto the surface of the wiring pattern 2formed of a silver sintered body. Herein, the palladium catalyst is alsoprovided to the silver particles 4 deposited on the surface of thewiring pattern formed of a silver sintered body in the silverprecipitation treatment step.

Next, the electroless multi-layered coating plating treatment step ofStep S104 is performed.

<Electroless Nickel Plating Step>

First, the electroless nickel plating step is described with referenceto FIGS. 5 and 6. FIG. 5 is a sectional view illustrating a state inwhich the surface of the wiring pattern 2 formed of a silver sinteredbody after the catalyzing step has been subjected to the electrolessnickel plating step. In addition, FIG. 6 is an enlarged viewillustrating the glass component 3 portion of FIG. 5 formed on thesurface of the wiring pattern 2 formed of a silver sintered body.

In the electroless nickel plating step of Step S1041, as illustrated inFIG. 5, an electroless nickel plating coating 5 is formed on the surfaceof the wiring pattern 2 formed of a silver sintered body. At this time,as illustrated in FIG. 6, the silver particles 4 deposited on the glasscomponent 3 are each in a state of being formed in the electrolessnickel plating coating 5.

As an electroless nickel plating liquid to be used in this step, anyplating liquid for electroless nickel plating heretofore known may beused. For example, there may be used a plating liquid containing 2 wt %of nickel sulfate as a metal salt, 2 wt % of sodium hypophosphite as areducing agent, and 10 wt % of citric acid, malic acid, succinic acid,or the like as a complexing agent, and having a pH adjusted to 4.5 withsulfuric acid or sodium hydroxide. In the present invention, the “wt %”refers to a value with respect to the entire prepared liquid, unlessotherwise stated.

As the electroless nickel plating conditions, the immersion time periodof the LTCC substrate in the electroless nickel plating liquid and theliquid temperature of the electroless nickel plating liquid mayappropriately be set so that the electroless nickel plating coatingachieves a desired thickness. For example, an electroless nickel platingcoating having a thickness of about 4 μm is obtained by setting theliquid temperature and the plating time period to 80° C. and 20 minutes,respectively.

<Electroless Palladium Plating Step>

Next, the electroless palladium plating step is described with referenceto FIG. 7. FIG. 7 is a sectional view illustrating a state in which thesurface of the wiring pattern 2 formed of a silver sintered body in thestate of FIG. 5 has been subjected to the electroless palladium platingstep.

In the electroless palladium plating step of Step S1042, as illustratedin FIG. 7, an electroless palladium plating coating 6 is formed on theelectroless nickel plating coating 5 formed in the electroless nickelplating step (S1041). As an electroless palladium plating liquid to beused in the step, a hypophosphorous acid-based palladium plating liquid,a phosphorous acid-based palladium plating liquid, or a formate-basedpalladium plating liquid, which has hitherto been used, may be used. Asthe hypophosphorous acid-based liquid, for example, the followingplating liquid is used: a plating liquid containing palladium chlorideas a metal salt, a palladium compound such as palladium acetate, sodiumhypophosphite as a reducing agent, an amine compound as a complexingagent such as ethylenediaminetetraacetic acid, a pH adjuster, and thelike.

As the electroless palladium plating conditions, the immersion timeperiod of the LTCC substrate in the electroless palladium plating liquidand the liquid temperature of the electroless palladium plating liquidmay appropriately be set so that the electroless palladium platingcoating 6 achieves a desired thickness. For example, in the case ofusing the hypophosphorous acid-based electroless palladium platingliquid, an electroless palladium plating coating 6 having a thickness ofabout 0.1 μm is obtained by setting the liquid temperature and theplating time period to 50° C. and 5 minutes, respectively.

<Substitution-Type Electroless Plating Step>

Next, a substitution-type electroless plating step is described withreference to FIG. 8. FIG. 8 is a sectional view illustrating a state inwhich the surface of the wiring pattern 2 formed of a silver sinteredbody in the state of FIG. 7 has been subjected to the substitution-typeelectroless plating step.

In the substitution-type electroless gold plating step of Step S1043, asillustrated in FIG. 8, a substitution-type electroless gold platingcoating 7 is formed on the electroless palladium plating coating 6formed in the electroless palladium plating step. As a substitution-typeelectroless gold plating liquid to be used in this step, acyanogen-based gold plating liquid or a gold sulfite-based gold platingliquid, which has hitherto been used, may be used. As the cyanogen-basedplating liquid, there may be used, for example, a plating liquidcontaining gold potassium cyanide as a metal salt,ethylenediaminetetraacetic acid, citric acid, or the like as acomplexing agent, a pH adjuster, and the like. In addition, as the goldsulfite-based plating liquid, there may be used a plating liquidcontaining gold sodium sulfite or the like as a metal salt, and sodiumsulfite, ethylenediamine, or the like as a complexing agent.

As the substitution-type electroless plating conditions, the immersiontime period of the LTCC substrate in the substitution-type electrolessgold plating liquid and the liquid temperature of the substitution-typeelectroless gold plating liquid may appropriately be set so that thesubstitution-type electroless gold plating coating achieves a desiredthickness. For example, in the case of using the cyanogen-basedsubstitution-type electroless gold plating liquid, a substitution-typeelectroless gold plating coating having a thickness of 0.05 μm isobtained by setting the liquid temperature and the plating time periodto 90° C. and 10 minutes, respectively. Thus, a glass ceramic substrateillustrated in FIG. 8 is obtained.

That is, as illustrated in FIG. 8, the glass ceramic substrate to beobtained through Steps S101 to S104 includes: the nickel plating coating5 formed on the wiring pattern 2 formed of a silver sintered bodyincluding the silver particles 4 deposited on the glass component 3 andthe glass component 3; the palladium plating coating 6 formed on thenickel plating coating 5; and the substitution-type gold plating coating7 formed on the palladium plating coating 6.

After the electroless plating treatment, the LTCC substrate is subjectedto wire bonding treatment, soldering, or the like, as an implementationstep.

Such electroless plating method, which includes, between the degreasingand activation step and the catalyzing step, the metal precipitationtreatment step of depositing the silver particles 4 on the glasscomponent 3 present on the surface of the wiring pattern 2 formed of asilver sintered body, allows the catalyst to be provided also to thedeposited silver particles 4. With this, non-plating during theelectroless nickel plating can be prevented. In addition, the wiringpattern 2 formed of a silver sintered body is well plated with nickel inthe electroless nickel plating step. Further, the surface of the wiringpattern 2 formed of a silver sintered body can be prevented from beingrecessed.

In addition, the formation of voids can be suppressed in the platingcoating, because the surface of the wiring pattern 2 formed of a silversintered body can be prevented from being recessed. With this, theplating liquid or washing liquid used during the plating can beprevented from being taken in the voids, and thus vaporization of thewater content during solder connection and accompanying solderconnection failure can be prevented. Thus, the LTCC substrate canachieve improved module reliability.

In addition, the use of the silver precipitation treatment liquid, whichcontains as a first reducing agent a phosphoric acid compound or anorganic acid and as a second reducing agent an inorganic compound atspecific concentrations and has a pH adjusted to from 4 to 6, allowssilver to be more reliably precipitated on the glass component 3 presenton the surface of the wiring pattern 2 formed of a silver sintered body.With this, the effects of suppressing the formation of voids in theplating coating and preventing the non-plating of the plating coatingcan be enhanced.

Further, the adhesion force between the wiring pattern 2 formed of asilver sintered body and the plating coating can be increased by ananchor effect of the plating coating. With this, the module reliabilityof the LTCC substrate can be improved.

According to the first embodiment, the metal precipitation treatmentstep is performed between the degreasing and activation step and thecatalyzing step, as described above. As a result, silver is precipitatedon the glass component present on the surface of the wiring patternformed of a silver sintered body, and thus the non-plating state causedby glass floating can be prevented. In consequence, the non-plating ofthe nickel plating coating can be prevented, and the formation of voidsin the plating coating, and accompanying solder connection failure canbe suppressed. Thus, improved module reliability can be achieved.

Second Embodiment

FIG. 9 illustrates a process flow according to a second embodiment ofthe present invention. In the first embodiment, the electroless platingmethod including the degreasing and activation step, the silverprecipitation treatment step, the catalyzing step, the electrolessnickel plating step, the electroless palladium plating step, and thesubstitution-type electroless gold plating step in this order isdescribed. In contrast, in the second embodiment, an electroless platingmethod including, in addition to the steps of the first embodiment, aglass etching step between the electroless nickel plating step and theelectroless palladium plating step is described.

When the wiring patterns 2 formed of a silver sintered body in the firstembodiment have a narrow space therebetween, for example, have a spaceof 10 μm or less, palladium may be anomalously deposited on thedeposited silver in the electroless palladium plating step, to cause ashort circuit between the patterns. Therefore, in the second embodiment,etching treatment is performed between the electroless nickel platingstep and the electroless palladium plating step. Other configurationsare the same as those in the first embodiment.

In FIG. 9, a degreasing and activation step of Step S201 is the samestep as Step S101 of FIG. 1 in the first embodiment.

In addition, a silver precipitation treatment step of Step S202 is thesame step as Step S102 of FIG. 1 in the first embodiment.

Further, a catalyzing step of Step S203 is the same step as Step S103 ofFIG. 1 in the first embodiment.

In addition, an electroless nickel plating step (Step S2041), anelectroless palladium plating step (Step S2042), and a substitution-typeelectroless gold plating step (Step S2043) in an electrolessmulti-layered coating plating treatment step of Step S204 are the samesteps as Step S1041, Step S1042, and Step S1043 in Step S104 of FIG. 1in the first embodiment, respectively.

It should be noted that the process flow of the second embodimentdiffers from that of the first embodiment in that a glass etchingtreatment step of Step S2044 is added between Step S2041 and Step S2042.Now, Step S2044 is hereinafter described in detail.

<Glass Etching Treatment Step>

In the glass etching treatment step of Step S2044, fine particles formedon glass ceramic between the wiring patterns 2 formed of a silversintered body, which cause a short circuit between the patterns, aredissolved and removed with a glass etching liquid, without damaging thesurface of the patterns.

The fine particles are, for example, metal fine particles having anaverage particle size of about from 0.05 μm to 0.5 μm derived from themetal sintered body serving as a constituent of the wiring pattern. Inthis case, where the metal sintered body is formed of a silver-palladiumalloy, silver fine particles are exemplified as the fine particles.

A glass etching liquid containing any of an inorganic acid, a fluoride,and an alkali metal hydroxide is preferably used as the glass etchingliquid to be used in the glass etching treatment step.

For example, hydrochloric acid or sulfuric acid is preferably used asthe inorganic acid, hydrogen fluoride or ammonium fluoride is preferablyused as the fluoride, and sodium hydroxide is preferably used as thealkali metal hydroxide.

It is more preferred to use any one of hydrochloric acid having aconcentration adjusted to from 2 to 6 wt %, sulfuric acid having aconcentration adjusted to from 5 to 15 wt %, hydrofluoric acid having aconcentration adjusted to from 0.1 to 0.5 wt %, an ammonium fluorideaqueous solution having a concentration adjusted to from 0.5 to 1.0 wt%, and a sodium hydroxide aqueous solution having a concentrationadjusted to from 2 to 6 wt %. Such glass etching liquid having aspecified concentration as described above can remarkably enhance theeffect of removing the fine particles.

The glass etching treatment conditions are described below. Theimmersion time period of the LTCC substrate in the glass etching liquidis not particularly limited because the immersion time period isaffected by the liquid temperature of the glass etching liquid or thelike, but is generally preferably from 3 to 5 minutes.

The highly acidic or highly basic glass etching liquid containing theinorganic acid or the alkali metal hydroxide can efficiently dissolveglass, which is generally difficult to be dissolved with any materialother than a fluoride, when the glass etching liquid is used at 40° C.or more. The liquid temperature is not particularly limited as long asthe etching can be performed, but is preferably adjusted to from 40° C.to 60° C. from the viewpoints of etching efficiency, protection of thewiring pattern, and the like.

A combination of the liquid temperature and treatment time period of theglass etching treatment is, for example, as follows: in the case ofusing as the glass etching liquid a 4 wt % sodium hydroxide aqueoussolution, the liquid temperature is preferably from 40 to 60° C., andthe treatment time period is preferably from 3 to 5 minutes.

Alternatively, the glass etching liquid containing the fluoride can beused for the treatment at room temperature, but may be used after beingadjusted to an appropriate temperature.

The fluoride can remove the fine particles through glass etching andrender the surface of the glass ceramic water repellent, and hence cansuppress the anomalous deposition of palladium. The glass ceramic isgenerally an oxide containing as a main component a silicate salt. Itsoutermost surface is terminated with a hydroxyl group, and hence ishydrophilic and highly reactive.

However, the terminal hydroxyl group attached to silicon in the glassceramic is terminated with hydrogen through treatment using the glassetching liquid containing the fluoride such as hydrofluoric acid. As aresult, the surface of the glass ceramic becomes hydrophobic as comparedto the case of the hydroxyl group-terminated glass ceramic, and thus hasa lower reactivity. In the case of using the etching liquid containingthe fluoride, the glass ceramic is dissolved, and as a result, the fineparticles, which cause the anomalous deposition of palladium, arelargely removed by liftoff, as in the case of using the etching liquidcontaining the inorganic acid or the alkali metal hydroxide.

Even when fine particles that are not removed by the treatment using thefluoride remain, the entire surface of the glass ceramic exhibits waterrepellent action by being terminated with hydrogen as described above,and thus has a low reactivity. As a result, the remaining fine particlesare prevented from being brought into contact with and reacting with theelectroless palladium plating liquid in the next step, and thuspalladium is prevented from being deposited on the fine particles.

In addition, other than the above-mentioned etching liquids, a highlyacidic organic acid such as maleic acid, or sodium carbonate, which ishighly basic, may be utilized as the glass etching liquid. In the caseof using such glass etching liquid, the concentration of the glassetching liquid, the liquid temperature and immersion time period of theetching treatment, and the like may be appropriately adjusted, as in thecase of using the etching liquid containing the inorganic acid, thealkali metal hydroxide, or the fluoride.

It should be noted that the glass etching liquid in the secondembodiment is substantially free of cyanogen and sulfur. The“substantially free of” means that cyanogen and sulfur are in no dangerof inducing inactivation or corrosion that damages a desired conductorpattern.

In addition, the “water repellent” in the second embodiment means thatthe surface is hydrophobic and has a low reactivity as compared to theone terminated with a hydroxyl group. The water repellency(hydrophobicity) may be compared based on a value determined by wettingangle measurement. The treatment using the fluoride can suppress theanomalous deposition of palladium by double effects of glass etching andinactivating the surface of the glass ceramic.

Further, in the second embodiment, the glass etching treatment step canremarkably enhance the effect of removing the fine particles bysubjecting the glass ceramic substrate to ultrasonic treatment while theglass ceramic substrate is immersed in the glass etching liquid. Inaddition, in the case of performing ultrasonic treatment as justdescribed, the immersion time period can be set shorter than usual.

A glass ceramic substrate to be thus obtained through Steps S201 to S204is the same as that to be obtained in the first embodiment. That is, asillustrated in FIG. 8, the glass ceramic substrate includes: the nickelplating coating 5 formed on the wiring pattern 2 formed of a silversintered body including the silver particles 4 deposited on the glasscomponent 3 and the glass component 3; the palladium plating coating 6formed on the nickel plating coating 5; and the substitution-type goldplating coating 7 formed on the palladium plating coating 6. Inaddition, the silver particles 4 deposited on the glass component 3 areformed in the nickel plating coating 5.

As described above, the electroless plating method according to thesecond embodiment, which includes the glass etching step between theelectroless nickel plating step and the electroless palladium platingstep, can suppress the deposition of palladium on the deposited silver.As a result, a short circuit between the patterns can be prevented.

Third Embodiment

FIG. 10 illustrates a process flow according to a third embodiment ofthe present invention. In the first embodiment, the electroless platingmethod including the electroless multi-layered coating plating treatmentstep including the electroless nickel plating step, the electrolesspalladium plating step, and the substitution-type electroless goldplating step in this order is described. In contrast, in the thirdembodiment, an electroless plating method including an electrolessmulti-layered coating plating treatment step including an electrolessnickel plating step, a substitution-type electroless gold plating step,and a reduction-type electroless gold plating step in this order isdescribed. Other configurations are the same as those in the firstembodiment.

In FIG. 10, Step S301, Step S302, and Step S303 are the same steps asStep S101, Step S102, and Step S103 of FIG. 1 in the first embodiment,respectively.

Next, an electroless multi-layered coating plating treatment step ofStep S304 is performed.

First, an electroless nickel plating step of Step S3041 is performed.Step S3041 is the same step as Step S1041 of FIG. 1 in the firstembodiment.

<Substitution-Type Electroless Gold Plating Step>

Next, a substitution-type electroless gold plating step is describedwith reference to FIG. 11. FIG. 11 is a sectional view illustrating astate in which the surface of the wiring pattern 2 formed of a silversintered body of FIG. 9 has been subjected to a substitution-typeelectroless gold plating step and a reduction-type electroless goldplating step.

In the substitution-type electroless gold plating step of Step S3042, asillustrated in FIG. 11, a substitution-type electroless gold platingcoating 7 is formed on the electroless nickel plating coating 5 formedin the electroless nickel plating step. The step prior to thesubstitution-type electroless gold plating step of Step S3042 differsfrom that in the first embodiment, but the substitution-type electrolessgold plating step is the same step as Step S1042 in the first embodimentand uses the same substitution-type gold plating liquid.

<Reduction-Type Electroless Gold Plating Step>

Next, in the reduction-type electroless gold plating step of Step S3043,as illustrated in FIG. 11, a reduction-type electroless gold platingcoating 8 is formed on the substitution-type electroless gold platingcoating 7 formed in the substitution-type electroless gold plating step.As a reduction-type electroless gold plating liquid to be used for theformation of the reduction-type electroless gold plating coating 8, acyanogen-based gold plating liquid or a gold sulfite-based gold platingliquid, which has hitherto been used, may be used.

As the cyanogen-based reduction-type electroless gold plating liquid,for example, a plating liquid containing gold potassium cyanide as asupply source of gold, potassium cyanide or the like as a complexingagent, and sodium hydroxide, dimethylamine borane, or the like as areducing agent, and having a pH adjusted to 13 is used. As the goldsulfite-based reduction-type gold plating liquid, for example, a platingliquid containing gold sodium sulfite as a supply source of gold, sodiumsulfite or sodium thiosulfate as a complexing agent, and ascorbic acidor the like as a reducing agent, and having a pH adjusted to 7 is used.

As the reduction-type electroless gold plating conditions, the immersiontime period of the LTCC substrate in the reduction-type electroless goldplating liquid and the liquid temperature of the reduction-typeelectroless gold plating liquid may appropriately be set so that theelectroless gold plating coating can achieve a desired thickness. Forexample, in the case of using the cyanogen-based reduction-typeelectroless gold plating liquid, an electroless gold plating coatinghaving a thickness of 0.7 μm is obtained by setting the liquidtemperature and the plating time period to 80° C. and 30 minutes,respectively. It should be noted that, in general, the reduction-typeelectroless gold plating coating 8 can be varied in thickness ascompared to the substitution-type electroless gold plating coating 7.For example, the reduction-type electroless gold plating coating 8 canbe formed to have a thickness of from 0.1 μm to 1.0 μm. Thus, a glassceramic substrate as illustrated in FIG. 11 is obtained.

As illustrated in FIG. 11, the glass ceramic substrate to be thusobtained through Steps S301 to S304 includes: the nickel plating coating5 formed on the wiring pattern 2 formed of a silver sintered bodyincluding the silver particles 4 deposited on the glass component 3 andthe glass component 3; the substitution-type electroless gold platingcoating 7 formed on the nickel plating coating 5; and the reduction-typegold plating coating 8 formed on the substitution-type electroless goldplating coating 7. In addition, the silver particles 4 deposited on theglass component 3 are formed in the nickel plating coating 5.

At the time of an implementation step after the plating treatment, theNi/Pd/Au plating coating of the first embodiment and the secondembodiment may cause a reduction in wire bonding pull strength, areduction in solder wettability, or the like depending on theimplementation step. However, in the electroless plating method of thethird embodiment, the electroless multi-layered coating platingtreatment step is not limited to include the electroless nickel platingstep, the electroless palladium plating step, and the substitution-typeelectroless gold plating step, and is intended to include theelectroless nickel plating step, the substitution-type electroless goldplating step, and the reduction-type electroless gold plating step.

Therefore, the plating coating formed on the surface of the wiringpattern 2 formed of a silver sintered body is not limited to theNi/Pd/Au plating coating, and it is possible to perform animplementation step that cannot be performed in the case of the Ni/Pd/Auplating coating. As a result, the implementation conditions can beexpanded.

According to the third embodiment, the electroless plating methodemploys as its final step the reduction-type electroless gold plating asdescribed above, and hence the gold plating coating can be formed tohave a large thickness. In addition, the electroless multi-layeredcoating plating treatment step is not limited to one method, andtherefore the kind of the multi-layered plating coating is not limited.As a result, the implementation conditions can be expanded to a widevariety of substrates.

Fourth Embodiment

FIG. 12 illustrates a process flow according to a fourth embodiment ofthe present invention. In the third embodiment, the electroless platingmethod including the degreasing and activation step, the metalprecipitation treatment step, the catalyzing step, the electrolessnickel plating step, the substitution-type electroless gold platingstep, and the reduction-type electroless gold plating step in this orderis described. In contrast, in the fourth embodiment, an electrolessplating method including, in addition to the steps of the thirdembodiment, a glass etching step between the substitution-typeelectroless gold plating step and the reduction-type electroless goldplating step is described.

As in the second embodiment, when the wiring patterns 2 formed of asilver sintered body have a narrow space therebetween, for example, havea space of 10 μm or less, gold may be anomalously deposited on thedeposited silver in the substitution-type electroless gold plating step,to cause a short circuit between the patterns. In contrast, in thefourth embodiment, etching treatment is performed between thesubstitution-type electroless gold plating step and the reduction-typeelectroless gold plating step. Other configurations are the same asthose in the third embodiment.

In FIG. 12, Step S401, Step S402, and Step S403 are the same steps asStep S301, Step S302, and Step S303 of FIG. 10 in the third embodiment,respectively.

In addition, an electroless nickel plating step (Step S4041), asubstitution-type electroless gold plating step (Step S4042), and areduction-type electroless gold plating treatment step (Step S4043) inan electroless multi-layered coating plating treatment step of Step S404are the same steps as Step S3041, Step S3042, and Step S3043 in StepS304 of FIG. 10 in the third embodiment, respectively.

It should be noted that the process flow of the fourth embodimentdiffers from that of the third embodiment in that a glass etchingtreatment step of Step S4044 is added between Step S4041 and Step S4042.Now, Step S4044 is hereinafter described in detail.

The glass etching treatment step of Step S4044 is the same step as StepS2044 of FIG. 9 in the second embodiment, and uses the same glassetching liquid.

The glass ceramic substrate to be thus obtained through Steps S401 toS404 is the same as that to be obtained in the third embodiment. Thatis, as illustrated in FIG. 11, the glass ceramic substrate includes: thenickel plating coating 5 formed on the wiring pattern 2 formed of asilver sintered body including the silver particles 4 deposited on theglass component 3 and the glass component 3; the substitution-typeelectroless gold plating coating 7 formed on the nickel plating coating5; and the reduction-type gold plating coating 8 formed on thesubstitution-type electroless gold plating coating 7. In addition, thesilver particles 4 deposited on the glass component 3 are formed in thenickel plating coating 5.

Such electroless plating method can suppress the anomalous deposition ofgold. As a result, a short circuit between the patterns can beprevented.

As described above, the electroless plating method according to thefourth embodiment can concurrently achieve the effects obtained in thesecond embodiment and third embodiment.

It should be noted that the methods according to the first embodiment tothe fourth embodiment each include a pure water washing treatment stepof washing the LTCC substrate by immersing the LTCC substrate in purewater between the respective steps. In addition, in the pure waterwashing treatment step, the LTCC substrate is preferably washed withpure water for about 1 minute.

In addition, the silver precipitation treatment step can remarkablyenhance a silver precipitating effect by subjecting the LTCC substrateto ultrasonic treatment while the LTCC substrate is immersed in thesilver precipitation treatment liquid. This is because that theultrasonic treatment promotes dissolution of the glass component 3, andultrasonic vibration promotes redeposition of the silver componentbecause the silver component eluted through the dissolution of the glasscomponent 3 is dissolved to be saturated in the silver precipitationtreatment liquid. Further, in the case of performing ultrasonictreatment as just described, the immersion time period can be setshorter than usual.

Further, the electroless plating methods according to the firstembodiment to the fourth embodiment can be applied not only to the LTCCsubstrate, but also to a wide variety of substrates.

In addition, the electroless plating coatings in the first embodiment tothe fourth embodiment are not limited to the Ni/Pd/Au plating coatingand the Ni/Au plating coating, and other multi-layered plating coatingscan be employed.

EXAMPLES

Table 1 shows operation conditions and results of examples using LTCCsubstrates corresponding to the first embodiment, the second embodiment,and Comparative Example. Table 2 shows operation conditions and resultsof Examples using LTCC substrates corresponding to the third embodimentand fourth embodiment. Table 3 shows operation conditions and results ofExamples using alumina ceramic substrates corresponding to the firstembodiment. Table 4 shows operation conditions and results of Examplesusing alumina ceramic substrates corresponding to the third embodiment.Table 5 shows anomalous deposition states of palladium or gold betweenpatterns in Examples 1 to 36 according to the present invention andComparative Examples 1 and 2.

The present invention is hereinafter described in detail by way ofExamples, but the present invention is not limited thereto.

Examples 1 to 6 First Embodiment

A LTCC substrate including the insulating base material 1 formed ofglass ceramic measuring 20 mm in width, 20 mm in length, and 500 μm inthickness, and a metal sintered body containing as a main componentsilver was used. The LTCC substrate was subjected to a degreasing andactivation treatment step, a silver precipitation treatment step, and acatalyzing step of providing a palladium catalyst in accordance with themethod described in the first embodiment. In the degreasing andactivation treatment step, the LTCC substrate was subjected todegreasing treatment by using EETOREX 72 (manufactured by ElectroplatingEngineers of Japan Ltd.), and then washed with pure water for 1 minute,followed by activation treatment by using EETOREX 62 (manufactured byElectroplating Engineers of Japan Ltd.).

After the substrate was immersed in pure water and left for 1 minute,the substrate was taken out therefrom, and subjected to the silverprecipitation treatment step in accordance with the first embodiment bychanging the silver precipitation treatment liquid, the liquidtemperature, the treatment time period, the presence or absence ofultrasonic treatment, and the time period of the ultrasonic treatment.Thus, the silver particles 4 were precipitated on the glass component 3present on the surface of the wiring pattern 2 formed of a silversintered body. As shown in Table 1, the changed conditions were asfollows: the concentrations of the first reducing agent and secondreducing agent in the silver precipitation treatment liquid were set to5 wt % and 10 ppm, respectively; the liquid temperature was set to 85°C.; and in addition, the following conditions of the precipitationtreatment time period, glass etching, and ultrasonic treatment werecombined.

Precipitation treatment time period: 1 minute, 5 minutes, or 10 minutesGlass etching: present or absentUltrasonic treatment: present or absent

After that, the substrate was immersed in pure water and left for 1minute, and then taken out therefrom, followed by being immersed inLECTROLESS AC-2 (manufactured by Electroplating Engineers of Japan Ltd.)for 1 minute. After that, the substrate was subjected to a washing stepby being immersed in pure water and left for 1 minute. Thus, thesubstrate was subjected to pretreatment steps.

Next, LECTROLESS NP7600 (manufactured by Electroplating Engineers ofJapan Ltd.) was used as a nickel plating liquid and was heated to 85° C.The substrate was immersed in the nickel plating liquid at thetemperature for 20 minutes in accordance with the coating formationmethod described in the first embodiment. Thus, the electroless nickelplating coating 5 having a thickness of 4 μm was formed on the wiringpattern 2 formed of a silver sintered body formed of a metal sinteredbody.

Then, after water washing treatment for 1 minute, the substrate wassubjected to the electroless palladium plating step in accordance withthe first embodiment, to form the electroless palladium plating coating6 having a thickness of 0.1 μm. After that, the substrate was subjectedto the electroless gold plating step, to form the electroless goldplating coating 7 having a thickness of 0.05 μm. In the electrolesspalladium plating step, LECTROLESS Pd2000S (manufactured byElectroplating Engineers of Japan Ltd.) was used, and the substrate wasimmersed therein under the condition of a liquid temperature of 50° C.for 10 minutes.

In addition, in the electroless gold plating step, LECTROLESS FX-5(manufactured by Electroplating Engineers of Japan Ltd.) was used, andthe substrate was immersed therein under the condition of a liquidtemperature of 85° C. for 5 minutes. It should be noted that thethickness of each of the plating coatings was measured by using an X-rayfluorescence film thickness measuring apparatus.

Examples 7 to 12 Second Embodiment

The same LTCC substrate as in Example 1 was used and subjected topretreatment steps of degreasing and activation treatment, providing apalladium catalyst, and the like in the same manner as in Example 1.After that, in accordance with the second embodiment, the substrate wassubjected to the electroless nickel plating step, and then subjected towater washing treatment for 1 minute. After that, the substrate wassubjected to glass etching treatment in accordance with the glassetching step described in the second embodiment. After that, thesubstrate was subjected to the electroless palladium plating step andthe substitution-type electroless gold plating step. The reagents usedin the steps were the same as in Example 1.

TABLE 1 Concentration of reducing agent Precipitation First SecondLiquid treatment reducing reducing temperature time period UltrasonicGlass agent (wt %) agent (ppm) (° C.) (min) treatment etching Example 15 10 85 1 Absent Absent 2 5 10 85 1 Present Absent 3 5 10 85 5 AbsentAbsent 4 5 10 85 5 Present Absent 5 5 10 85 10 Absent Absent 6 5 10 8510 Present Absent 7 5 10 85 1 Absent Present 8 5 10 85 1 Present Present9 5 10 85 5 Absent Present 10 5 10 85 5 Present Present 11 5 10 85 10Absent Present 12 5 10 85 10 Present Present Comparative 1 5 10 85 1Absent Absent Example

Examples 13 to 18 Third Embodiment

The same LTCC substrate as in Example 1 was used and subjected topretreatment steps of degreasing and activation treatment, providing apalladium catalyst, and the like in the same manner as in Example 1.After that, in accordance with the third embodiment, the substrate wassubjected to the electroless nickel plating step, and then subjected towater washing treatment for 1 minute. After that, the substrate wassubjected to the electroless gold plating step in accordance with thethird embodiment, and then subjected to water washing treatment for 1minute. After that, the substrate was subjected to the reduction-typeelectroless gold plating step in accordance with the third embodiment,to form the reduction-type electroless gold plating coating 8 having athickness of 0.1 μm. In the reduction-type electroless plating step,LECTROLESS FX-5 (manufactured by Electroplating Engineers of Japan Ltd.)was used, and the substrate was immersed therein under the condition ofa liquid temperature of 85° C. for 10 minutes. Besides, the reagentsused in the steps were the same as in Example 1.

Examples 19 to 24 Fourth Embodiment

The same LTCC substrate as in Example 1 was used and subjected topretreatment steps of degreasing and activation treatment, providing apalladium catalyst, and the like in the same manner as in Example 1.After that, in accordance with the fourth embodiment, the substrate wassubjected to the electroless nickel plating step, and then subjected towater washing treatment for 1 minute. After that, the substrate wassubjected to glass etching treatment in accordance with the glassetching step described in the fourth embodiment. After that, thesubstrate was subjected to the electroless gold plating step and thereduction-type electroless gold plating step. The reagents used in thesteps were the same as in Example 1.

TABLE 2 Concentration of reducing agent Precipitation First SecondLiquid treatment reducing reducing temperature time period UltrasonicGlass agent (wt %) agent (ppm) (° C.) (min) treatment etching Example 135 10 85 1 Absent Absent 14 5 10 85 1 Present Absent 15 5 10 85 5 AbsentAbsent 16 5 10 85 5 Present Absent 17 5 10 85 10 Absent Absent 18 5 1085 10 Present Absent 19 5 10 85 1 Absent Present 20 5 10 85 1 PresentPresent 21 5 10 85 5 Absent Present 22 5 10 85 5 Present Present 23 5 1085 10 Absent Present 24 5 10 85 10 Present Present Comparative 2 5 10 851 Absent Absent Example

Examples 25 to 30 First Embodiment

An alumina ceramic substrate including the insulating base material 1formed of alumina ceramic measuring 20 mm in width, 20 mm in length, and500 μm in thickness, and a metal sintered body containing as a maincomponent tungsten or molybdenum was used. The alumina ceramic substratewas treated in accordance with the first embodiment, and the degreasingand activation treatment was performed by using ETW (manufactured byWORLD METAL Co., Ltd.).

The substrate was immersed in pure water and left for 1 minute, and thentaken out therefrom. After that, the substrate was subjected topretreatment steps of precipitation treatment and providing a palladiumcatalyst in the same manner as in Example 1 in accordance with the firstembodiment. After that, in accordance with the first embodiment, thesubstrate was subjected to the electroless nickel plating step and thensubjected to water washing treatment for 1 minute, followed by beingsubjected to the electroless palladium plating step and thesubstitution-type electroless gold plating step. The reagents used inthe steps were the same as in Example 1, except for the reagent in thedegreasing and activation step.

TABLE 3 Concentration of reducing agent Precipitation First SecondLiquid treatment reducing reducing temperature time period UltrasonicGlass agent (wt %) agent (ppm) (° C.) (min) treatment etching Example 255 10 85 1 Absent Absent 26 5 10 85 1 Present Absent 27 5 10 85 5 AbsentAbsent 28 5 10 85 5 Present Absent 29 5 10 85 10 Absent Absent 30 5 1085 10 Present Absent

Examples 31 to 36 Third Embodiment

The same alumina ceramic substrate as in Example 25 was used andsubjected to pretreatment steps of degreasing and activation treatmentand providing a palladium catalyst in the same manner as in Example 25.After that, in accordance with the third embodiment, the substrate wassubjected to the electroless nickel plating step, and then subjected towater washing treatment for 1 minute. After that, the substrate wassubjected to the electroless gold plating step in accordance with thethird embodiment and then subjected to water washing treatment for 1minute, followed by being subjected to the reduction-type electrolessgold plating step in accordance with the third embodiment. The reagentsused in the steps were the same as in Example 1.

TABLE 4 Concentration of reducing agent Precipitation First SecondLiquid treatment reducing reducing temperature time period UltrasonicGlass agent (wt %) agent (ppm) (° C.) (min) treatment etching Example 315 10 85 1 Absent Absent 32 5 10 85 1 Present Absent 33 5 10 85 5 AbsentAbsent 34 5 10 85 5 Present Absent 35 5 10 85 10 Absent Absent 36 5 1085 10 Present Absent

Comparative Example 1

The same LTCC substrate as in Example 1 was used and subjected toelectroless plating. The difference from Example 1 was that the silverprecipitation treatment step was omitted, and other conditions wereexactly the same as in Example 1.

Comparative Example 2

The same LTCC substrate as in Example 13 was used and subjected toelectroless plating. The difference from Example 13 was that the silverprecipitation treatment step was omitted, and other conditions wereexactly the same as in Example 13.

The presence or absence of voids shown in Table 5 was determined bycross section processing of the wiring pattern by focused ion beam (FIB)after the electroless plating, followed by observation of the crosssection by scanning ion microscopy (SIM) (at a magnification of from 100to 500). The glass component 3 was measured at 10 points, and the numberof voids right above the glass component 3 was counted.

The evaluation results shown in Table 5 revealed that, in ComparativeExamples 1 and 2, in which electroless plating was performed withoutperforming the silver precipitation treatment step, voids were generatedin the nickel plating coating 5, but in Examples 1 to 36 correspondingto the first embodiment to the fourth embodiment of the presentinvention, in which the silver precipitation treatment step wasperformed, voids were hardly observed in the nickel plating coating 5.

In addition, the presence or absence of anomalous deposition state ofpalladium or gold between the patterns shown in Table 5 was determinedby stereoscopic microscope observation (at a magnification of from 100to 500). The case where the anomalous deposition accounted for 0% ormore and less than 10% of the observation area was defined as noanomalous deposition, and was represented by Symbol “0” in Table 5. Inaddition, the case where the anomalous deposition accounted for 10 ormore % and less than 50% of the observation area was defined as partialoccurrence (to the extent that a short circuit does not occur), and wasrepresented by Symbol “A” in Table 5. The case where the anomalousdeposition accounted for more than 50% of the observation area wasdefined as occurrence on almost the entire surface, and was representedby Symbol “x” in Table 5.

TABLE 5 Number of voids Anomalous deposition (point(s)) state betweenpatterns Example 1 1 Δ 2 0 Δ 3 0 Δ 4 0 Δ 5 0 Δ 6 0 x 7 1 ∘ 8 0 ∘ 9 0 ∘10 0 ∘ 11 0 ∘ 12 0 ∘ 13 1 Δ 14 0 Δ 15 0 Δ 16 0 Δ 17 0 Δ 18 0 x 19 2 ∘ 200 ∘ 21 0 ∘ 22 0 ∘ 23 0 ∘ 24 0 ∘ 25 3 ∘ 26 2 ∘ 27 1 ∘ 28 0 ∘ 29 0 ∘ 30 0∘ 31 3 ∘ 32 2 ∘ 33 1 ∘ 34 0 ∘ 35 0 ∘ 36 0 ∘ Comparative 1 7 Δ Example 28 Δ

While the first embodiment to the fourth embodiment and Examples of thepresent invention have been described above, the configurations of thefirst embodiment to the fourth embodiment and Examples may beappropriately combined.

1. An electroless plating method for a glass ceramic substratecomprising an insulating base material formed of glass ceramic, and awiring pattern formed of a silver sintered body, the electroless platingmethod comprising: a degreasing and activation treatment step ofdegreasing and activating a surface of the wiring pattern formed of asilver sintered body; a catalyzing step of providing a catalyst onto thesurface of the wiring pattern formed of a silver sintered body after thedegreasing and activation treatment step; and an electrolessmulti-layered coating plating treatment step of forming a multi-layeredelectroless plating coating on the surface of the wiring pattern formedof a silver sintered body on which the catalyst is provided, theelectroless plating method further comprising, between the degreasingand activation treatment step and the catalyzing step, a silverprecipitation treatment step of precipitating silver on a glasscomponent present on the surface of the wiring pattern formed of asilver sintered body after the degreasing and activation treatment step,the catalyzing step comprising providing the catalyst also to the silverprecipitated in the silver precipitation treatment step.
 2. Anelectroless plating method according to claim 1, wherein the electrolessmulti-layered coating plating treatment step comprises: an electrolessnickel plating step of forming an electroless nickel plating coating onthe surface of the wiring pattern formed of a silver sintered body onwhich the catalyst is provided; an electroless palladium plating step offorming an electroless palladium plating coating on the electrolessnickel plating coating; and a substitution-type electroless gold platingstep of forming a substitution-type electroless gold plating coating onthe electroless palladium plating coating.
 3. An electroless platingmethod according to claim 2, further comprising, between the electrolessnickel plating step and the electroless palladium plating step, a glassetching treatment step of dissolving fine particles formed on glassceramic with a glass etching liquid to remove the fine particles.
 4. Anelectroless plating method according to claim 1, wherein the electrolessmulti-layered coating plating treatment step comprises: an electrolessnickel plating step of forming an electroless nickel plating coating onthe surface of the wiring pattern formed of a silver sintered body onwhich the catalyst is provided; a substitution-type electroless goldplating step of forming a substitution-type electroless gold platingcoating on the electroless nickel plating coating; and a reduction-typeelectroless gold plating step of forming a reduction-type electrolessgold plating coating on the substitution-type electroless gold platingcoating.
 5. An electroless plating method according to claim 4, furthercomprising, between the electroless nickel plating step and thesubstitution-type electroless gold plating step, a glass etchingtreatment step of dissolving fine particles formed on glass ceramic witha glass etching liquid to remove the fine particles.
 6. An electrolessplating method according to claim 1, wherein the silver precipitationtreatment step comprises: using, as reducing agents, a phosphoric acidcompound and an organic acid as first reducing agents, and an inorganiccompound as a second reducing agent; and using a silver precipitationtreatment liquid containing any one of the first reducing agents or acombination of any one of the first reducing agents and the secondreducing agent.
 7. An electroless plating method according to claim 6,wherein the phosphoric acid compound comprises hypophosphorous acid,sodium hypophosphite, or potassium hypophosphite.
 8. An electrolessplating method according to claim 6, wherein the organic acid comprisesformic acid or citric acid.
 9. An electroless plating method accordingto claim 6, wherein the inorganic compound comprises iron(II) chloride,iron(II) sulfate, or sodium thiosulfate.
 10. A glass ceramic substrate,comprising an insulating base material formed of glass ceramic, and awiring pattern formed of a silver sintered body, precipitated silverbeing scattered in a particulate form on a glass component present on asurface of the wiring pattern formed of a silver sintered body, a nickelplating coating being formed on the wiring pattern formed of a silversintered body including the glass component and the silver scattered onthe glass component, a palladium plating coating being formed on thenickel plating coating, a gold plating coating being formed on thepalladium plating coating.
 11. A glass ceramic substrate, comprising aninsulating base material formed of glass ceramic, and a wiring patternformed of a silver sintered body, precipitated silver being scattered ina particulate form on a glass component present on a surface of thewiring pattern formed of a silver sintered body, a nickel platingcoating being formed on the wiring pattern formed of a silver sinteredbody including the glass component and the silver scattered on the glasscomponent, a gold plating coating being formed on the nickel platingcoating.
 12. A glass ceramic substrate according to claim 10 or 11,wherein the silver scattered in a particulate form on the glasscomponent present on the surface of the wiring pattern formed of asilver sintered body has a particle size of from 10 to 100 nm.
 13. Aglass ceramic substrate according to claim 11, wherein the silverscattered in a particulate form on the glass component present on thesurface of the wiring pattern formed of a silver sintered body has aparticle size of from 10 to 100 nm.